Panthalassa, also known as the Panthalassic or Panthalassan Ocean,
(from Greek πᾶν "all" and θάλασσα "sea"),[1] was the
superocean that surrounded the supercontinent Pangaea. During the
Paleozoic—
MesozoicMesozoic transition c. 250 Ma it occupied almost 70%
of Earth's surface. Its ocean-floor has completely disappeared because
of the continuous subduction along the continental margins on its
circumference.[2]
PanthalassaPanthalassa is also referred to as the Paleo-Pacific
("old Pacific") or Proto-Pacific because the
Pacific OceanPacific Ocean developed
from its centre in the
MesozoicMesozoic to the present.

The supercontinent
RodiniaRodinia began to break-up 870–845 Ma
probably as a consequence of a superplume caused by mantle slab
avalanches along the margins of the supercontinent. In a second
episode c. 750 Ma the western half of
RodiniaRodinia started to rift
part: western Kalahari and South China) broke away from the western
margins of Laurentia; and by 720 Ma Australia and East Antarctica
had also separated.[3] In the Late Jurassic the Pacific Plate opened
originating from a triple junction between the Panthalassic Farallon,
Phoenix, and Izanagi plates.
PanthalassaPanthalassa can be reconstructed based on
magnetic lineations and fracture zones preserved in the western
Pacific.[4]
In western
LaurentiaLaurentia (North America), a tectonic episode that preceded
this rifting produced failed rifts that harboured large depositional
basins in Western Laurentia. The global ocean of Mirovia, an ocean
that surrounded Rodinia, started to shrink as the Pan-African ocean
and
PanthalassaPanthalassa expanded.
Between 650 million and 550 million years ago, another supercontinent
started to form: Pannotia, which was shaped like a "V". Inside the "V"
was Panthalassa, outside of the "V" were the
Pan-African Ocean and
remnants of the
MiroviaMirovia Ocean.
Reconstruction of ocean basin[edit]
Most of the oceanic plates that formed the ocean floor of Panthalassa
have been subducted and traditional plate tectonic reconstructions
based on magnetic anomalies can therefore only be used for remains
from the
CretaceousCretaceous and later. The former margins of the ocean,
however, contain allochthonous terranes with preserved
Triassic–Jurassic intra-Panthalassic volcanic arcs, including
Kolyma–Omolon (northeast Asia), Anadyr–Koryak (east Asia),
Oku–Niikappu (Japan), and
Wrangellia and
Stikinia (western North
America). Furthermore, seismic tomography is being used to identify
subducted slabs in the mantle, from which the location of former
Panthalassic subduction zones can be derived. A series of such
subduction zones, called Telkhinia, defines two separate oceans or
systems of oceanic plates — the Pontus and Thalassa oceans.[5]
Named marginal oceans or oceanic plates include (clockwise)
Mongol-Okhotsk (now a suture between Mongolia and Sea of Okhotsk),
Oimyakon (between Asian craton and Kolyma-Omolon), Slide Mountain
Ocean (British Columbia),[6] and Mezcalera (western Mexico).
Eastern margin[edit]
The western margin (modern coordinates) of
LaurentiaLaurentia originated during
the Neoproterozoic break-up of Rodinia. The North American Cordillera
is an accretionary orogen which grew by the progressive addition of
allochthonous terranes along this margin from the Late Palaeozoic.
Devonian back-arc volcanism reveals how this eastern Panthalassic
margin developed into the active margin it still is in the
mid-Palaeozoic. Most of the continental fragments, volcanic arcs, and
ocean basins added to
LaurentiaLaurentia this way contained faunas of Tethyan
or Asian affinity. Similar terranes added to the northern Laurentia,
in contrast, have affinities with Baltica, Siberia, and the northern
Caledonies. These latter terranes were probably accreted along the
eastern
PanthalassaPanthalassa margin by a Caribbean–Scotia-style subduction
system.[7]
Western margin[edit]
The evolution of the Panthalassa–Tethys boundary is poorly known
because little oceanic crust is preserved — both the Izanagi
and the conjugate
Pacific OceanPacific Ocean floor is subducted and the ocean ridge
that separated them probably subducted c. 60–55 Ma. Today the
region is dominated by the collision of the
Australian PlateAustralian Plate with a
complex network of plate boundaries in south-east Asia, including the
SundalandSundaland block. Spreading along the Pacific-Phoenix ridge ended
83 Ma at the Osbourn Trough at the Tonga-Kermadec Trench.[4]
During the Permian atolls developed near the Equator on the
mid-Panthalassic seamounts. As
PanthalassaPanthalassa subducted along its western
margin during the Triassic and Early Jurassic, these seamounts and
palaeo-atolls were accreted as allochthonous limestone blocks and
fragments along the Asian margin.[8] One such migrating atoll complex
now form a 2-kilometre-long (1.2 mi) and 100-to-150-metre-wide
(330–490 ft) body of limestone in central Kyushu, south-west
Japan.[9]
Fusuline foraminifera, a now extinct order of single-celled organisms,
developed gigantism — the genus Eopolydiexodina, for example,
reached up to 16 cm (6.3 in) in size — and structural
sophistication, including symbiont relationships with
photosynthesising algae, during the Late Carboniferous and Permian.
The
Permian–Triassic extinction eventPermian–Triassic extinction event c. 260 Ma, however, put
an end to this development with only dwarf taxa persisting throughout
the Permian until the final fusuline extinction c. 252 Ma.
Permian fusulines also developed a remarkable provincialism by which
fusulines can be grouped into six domains.[10] Because of the large
size of
PanthalassaPanthalassa a hundred million years could separate the
accretion of different groups of fusulines. Assuming a minimum
accretion rate of 3 centimetres per year (1.2 in/year), the
seamount chains on which these groups evolved would be separated by at
least 3,000 km (1,900 mi) — these groups apparently
evolved in completely different environments.[11] A significant
sea-level drop at the end of the Permian led to the end-Capitanian
extinction event. The cause for this extinction is disputed, but a
likely candidate is an episode of global cooling which transformed
large amount of sea-water into continental ice.[12]
Seamounts accreted in eastern Australia as parts of the New England
orogen reveal the hotspot history of Panthalassa.[13] From the Late
Devonian to the Carboniferous
GondwanaGondwana and
PanthalassaPanthalassa converged along
the eastern margin of Australia along a west-dipping subduction system
which produced (west to east) a magmatic arc, a fore-arc basin, and an
accretionary wedge. Subduction ceased along this margin in the Late
Carboniferous and jumped eastward. From the Late Carboniferous to the
Early Permian the New England orogen was dominated by an extensional
setting related to a subduction to strike-slip transition. Subduction
was re-initiated in the Permian and the granitic rocks of the New
England
BatholithBatholith were produced by a magmatic arc, indicating the
presence of an active plate margin along most of the orogen. Permian
to
CretaceousCretaceous remains of this convergent margin, preserved as
fragments in Zealandia (New Zealand, New Caledonia, and the Lord Howe
Rise), were rifted off Australia during the Late
CretaceousCretaceous to Early
Tertiary break-up of eastern
GondwanaGondwana and the opening of the Tasman
Sea.[14] The
CretaceousCretaceous Junction Plate, located north of Australia,
separated the eastern Tethys from Panthalassa.[15]
Palaeo-oceanography[edit]
PanthalassaPanthalassa was a hemisphere-sized ocean, much larger than the modern
Pacific. It could be expected that the large size would result in
relatively simple ocean current circulation patterns, such as a single
gyre in each hemisphere, and a mostly stagnant and stratified ocean.
Modelling studies, however, suggest that an east-west sea surface
temperature (SST) gradient was present in which the coldest water was
brought to the surface by upwelling in the east while the warmest
water extended west into the Tethys Ocean. Subtropical gyres dominated
the circulation pattern. The two hemispherical belts were separated by
the undulating
Intertropical Convergence ZoneIntertropical Convergence Zone (ITCZ).[16]
In northern
PanthalassaPanthalassa there was mid-latitude westerlies north of
60°N with easterlies between 60°N and the Equator. Atmospheric
circulation north of 30°N is associated with the North Panthalassa
High which created Ekman convergence between 15°N and 50°N and Ekman
divergence between 5°N and 10°N. A pattern which resulted in
northward
Sverdrup transportSverdrup transport in divergence regions and southward in
convergence regions. Western boundary currents resulted in an
anti-cyclonic subtropical North
PanthalassaPanthalassa gyre at mid-latitudes and
a meridional anti-cyclonic circulation centred on 20°N.[16]
In tropical northern
PanthalassaPanthalassa trade winds created westward flows
while equatorward flows were created by westerlies at higher
latitudes. Consequently, trade winds moved water away from Gondwana
towards
LaurasiaLaurasia in the northern
PanthalassaPanthalassa Equatorial Current. When
the western margins of
PanthalassaPanthalassa were reached intense western
boundary currents would form the Eastern
LaurasiaLaurasia Current. At
mid-latitudes the North
PanthalassaPanthalassa Current would bring the water back
east where a weak Northwestern
GondwanaGondwana Current would finally close
the gyre. The accumulation of water along the western margin coupled
with the
Coriolis effectCoriolis effect would have created a
PanthalassaPanthalassa Equatorial
Counter Current.[16]
In the southern
PanthalassaPanthalassa the four currents of the subtropical gyre,
the South
PanthalassaPanthalassa Gyre, rotated counterclockwise. The South
Equatorial
PanthalassaPanthalassa Current flowed westward between the Equator and
10°S into the western, intense South Panthalasssa Current. The South
Polar Current then completes the gyre as the Southwestern Gondwana
Current. Near the poles easterlies created a subpolar gyre that
rotated clockwise.[16]
See also[edit]